How are tornadoes formed?

Question

U.K (AS level detail)

U.S.A (College level detail)

Answer 1

Supercells form when cold polar air meets warm tropical air. The result is a great instability caused by the rising warm air. A squall line, or narrow zone of cumulonimbus clouds forms, giving life to the tornadoes. Lightning flashes, and heavy rains and hail begin to fall. Soon after, the easiest recognizable part of the tornado, the funnel, seems to descend from the base of the cloud. In actuality, it does not, but rather the pressure within the cloud drops due to the increasing wind speeds. This is known as Bernoulli's principle. As the pressure drops, it causes moisture in the air to condense. This action continues down the spiral, giving the impression that the funnel is descending from the cloud base. In addition to the visible funnel, there is also a hissing sound, which turns into a loud roar when the tornado touches the earth.

Many people believe that there is no tornado unless there is a visible funnel cloud. However this is not true, for 'invisible' tornadoes can exist. Its the same thing as a normal tornado, but the funnel cloud does not descend to the ground. The latter situation is extremely rare.

Once the tornado reaches the ground, it starts to up debris around it. This can actually change the color of the tornado, because some dirt in the southern states is actually a deep shade of red

Ps i got this off of

http://library.thinkquest.org/16132/html...

I live in Oklahoma in smack dab of tornadoe alley if you have any questions of damadge left from tornadoes im your girl

email me if thats what you need

[e-mail]

Lauren~~~

Answer 2

They are formed when a super cell has a bow echo and that the rotation forms a core which all of the wind goes around the core of the tornado

Answer 3

These small, severe storms form several thousand feet above Earth's surface, usually during warm, humid, unsettled weather, and usually in conjunction with a severe thunderstorm. Sometimes a series of two or more tornadoes is associated with a parent thunderstorm. As the thunderstorm moves, tornadoes may form at intervals along its path, travel for a few miles, then dissipate. The forward speed of tornadoes has been observed to range from almost no motion to 70 mph.

The winds of some tornadoes have been estimated to exceed 300 mph. (Photo courtesy of NOAA Photo Library, NOAA Central Library; OAR/ERL/National Severe Storms Laboratory (NSSL).)

HOW A TORNADO IS FORMED

Tornado formation requires the presence of layers of air with contrasting characteristics of temperature, moisture, density, and wind flow. Complicated energy transformations produce the tornado vortex.

Many theories have been advanced as to the type of energy transformation necessary to generate a tornado, and none has won general acceptance. The two most frequently encountered theories visualize tornado generation as either the effect of thermally induced rotary circulations, or as the effect of converging rotary winds. Currently, scientists seem to agree that neither process generates tornadoes independently. It is more probable that tornadoes are produced by the combined effects of thermal and mechanical forces, with one or the other force being the stronger generating agent.

Numerous observations of lightning strokes and a variety of luminous features in and around tornado funnels have led scientists to speculate about the relationship between tornado formation and thunderstorm electrification. This hypothesis explores the alternative possibilities that atmospheric electricity accelerates rotary winds to tornado velocities, or that those high-speed rotary winds generate large electrical charges. Here, as in most attempts to understand complex atmospheric relationships, the reach of theory exceeds the grasp of proof.

SIZE, SPEED, & DURATION

Tornadoes vary greatly in size, intensity, and appearance. Most (69%) of the tornadoes that occur each year fall into the "weak" category. Wind speeds are in the range of 110 mph or less. Weak tornadoes account for less than 5% of all tornado deaths.

About one out of every three tornadoes (29%) is classified as "strong." Strong tornadoes have wind speeds reaching about 205 mph, with an average path length of 9 mi, and a path width of 200 yd. Almost 30% of all tornado deaths occur each year from this type of storm. Nearly 70% of all tornado fatalities, however, result from "violent" tornadoes. Although very rare (only about 2% are violent), these extreme tornadoes can last for hours. Average path lengths and widths are 26 mi and 425 yd, respectively. The largest of these may exceed a mile or more in width, with wind speeds approaching 300 mph.

Tornado Characteristics

Time of day during which tornadoes are most likely to occur is mid-afternoon, generally 3–7 P.M., but they have occurred at all times of day.

Direction of movement is usually from southwest to northeast. (Note: Tornadoes associated with hurricanes may move from an easterly direction.)

Length of path averages 4 mi, but may reach 300 mi. A tornado traveled 293 mi across Illinois and Indiana on May 26, 1917, and lasted seven hours and 20 minutes.

Width of path averages about 300–400 yd but tornadoes have cut paths a mile or more in width.

Speed of travel averages 25–40 mph, but speeds ranging from stationary to 68 mph have been reported.

The cloud directly associated with a tornado is a dark, heavy cumulonimbus (the familiar thunderstorm cloud) from which a whirling funnel-shaped pendant extends to the ground.

Precipitation associated with the tornado usually occurs first as rain just preceding the storm, frequently with hail, and as a heavy downpour immediately to the side of the tornado's path.

Sound occurring during a tornado has been described as a roaring, rushing noise, closely approximating that made by a train speeding through a tunnel or over a trestle, or the roar of many airplanes.

Tornado Intensity Rating System

The intensity of tornadoes is defined according to the Fujita Scale (or F scale), which ranges from F0 to F6 as outlined below.

F0: 40–72 mph winds. Damage is light and might include damage to tree branches, chimneys, and billboards. Shallow-rooted trees may be pushed over.

F1: 73–112 mph winds. Damage is moderate; mobile homes may be pushed off foundations and moving autos pushed off the road.

F2: 113–157 mph winds. Damage is considerable. Roofs can be torn off houses, mobile homes demolished, and large trees uprooted.

F3: 158–206 mph winds. Damage is severe. Even well-constructed houses may be torn apart, trees uprooted, and cars lifted off the ground.

F4: 207–260 mph winds. Damage is devastating. Houses can be leveled and cars thrown; objects become deadly missiles.

F5: 261–318 mph winds. Damage is incredible. Structures are lifted off foundations and carried away; cars become missiles. Fewer than 2% of all tornadoes reach an intensity of this magnitude.

F6: The maximum tornado wind speeds are not expected to exceed 318 mph.

Answer 4

i don't know exactly, but it's formed because high difference of pressure in land and sea. This fact being america and other land around there have many tornadoes.

Answer 5

I think tornadoes are formed when a thundercloud appears and then there is a lot of wind.  The wind begins to rotate in a circle and it picks up dirt and all that stuff.

Answer 6

Most tornadoes are spawned from supercell thunderstorms. Supercell thunderstorms are characterized by a persistent rotating updraft and form in environments of strong vertical wind shear.

Wind shear is the change in wind speed and/or direction with height.

The updraft lifts the rotating column of air created by the speed shear. This provides two different rotations to the supercell; cyclonic or counter clockwise rotation and an anti-cyclonic of clockwise rotation.

The directional shear amplifies the cyclonic rotation and diminishes the anti-cyclonic rotation

All that remains is the cyclonic rotation called a mesocyclone. By definition a supercell is a rotating thunderstorm.

When viewed from the top, the counter-clockwise rotation of the mesocyclone gives the supercell its classic "hook" appearence when seen by radar. As the air rises in the storm, it becomes stretched and more narrow with time.

The exact processes for the formation of a funnel are not known yet. Recent theories suggest that once a mesocyclone is underway, tornado development is related to the temperature differences across the edge of downdraft air wrapping around the mesocyclone.

However, mathematical modelling studies of tornado formation also indicate that it can happen without such temperature patterns; and in fact, very little temperature variation was observed near some of the most destructive tornadoes in history on May 3, 1999 in Oklahoma.

LEARN MORE about Tornado's

http://www.srh.noaa.gov/jetstream/tstorm...

http://www.srh.noaa.gov/jetstream/tstorm...

http://www.spc.noaa.gov/faq/tornado/

http://www.nssl.noaa.gov/faq/faq_tor.php

http://www.srh.noaa.gov/srh/jetstream/ts...

http://www.srh.noaa.gov/srh/jetstream/ts...

http://www.spc.noaa.gov/faq/tornado/

http://www.nssl.noaa.gov/faq/faq_tor.php

http://www.usatoday.com/weather/tornado/...

http://library.thinkquest.org/03oct/0075...

http://www.hubbard.lib.oh.us/tornado/tor...

http://www.tornadohistoryproject.com/

http://www.nssl.noaa.gov/hazard/

Tornado Climatology

http://www.nssl.noaa.gov/briefings/vol2_...

Answer 7

Well, in a nutshell, it's formed by ample instability, the turning of strong winds, and colder air above warmer air.